Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “allosteric modulation”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 901 records · Page 50Linked to original sources
PubMed1984

Structure and function of hemoglobin from Urechis caupo.

The hemoglobin of the erythrocytes of Urechis caupo is tetrameric. Three chromatographic fractions have been isolated. Fractions F-I (the major fraction) and F-II are each composed of at least five electrophoretic components. Minor fractions F-III has an amino acid composition which is very different from those of fractions F-I and F-II. Amino acid analysis and peptide mapping suggests that fractions F-I and F-II are very similar, and may differ only in a few post-translational modifications. The major fraction, F-I, appears to consist of tetramers in which all subunits are almost identical. Oxygen binding is noncooperative, with a pressure of half-saturation (p50) of 12 mm Hg at 20 degrees C and pH 7.5 in Tris buffers. The oxygen equilibria of undialyzed lysate and of hemoglobin purified by chromatography on Sephadex G-100 are identical. This observation indicates that no allosteric modulator is present. The oxygen equilibrium is not significantly affected by ATP, Cl-, Ca2+, Mg2+, or CO2. The pH dependence of oxygen binding is extremely small: delta Log p50/delta pH is only +0.06 between pH 6 and 7.5. The p50 value changes by no more than 15% between 6.8 microM and 4.3 mM (heme). The apparent enthalpy of oxygenation, delta H, is -11 kcal/mol. Deoxygenation, oxidation, dilution, or pH changes have no significant effect on the state of aggregation. These oxygen-binding properties are consistent with the suggestion that the primary function of the hemoglobin is to store oxygen during the hypoxia which occurs in the burrows of the animal at low tide.

Amino Acid Sequence↗
PubMed1987

Insulin stimulation of adipocyte membrane glucose transport. A graded biologic response insensitive to bilayer lipid disordering.

Aspects of the mechanism by which insulin stimulates the membrane glucose transport system were examined by assessing the influence of the bilayer lipid structure on transport stimulation characteristics, and considering the form of the insulin dose-response curve. We tested the effects of membrane lipid perturbation on the insulin stimulation process. Benzyl alcohol, at concentrations (25 mM) that grossly fluidize lipids forming the adipocyte membrane bilayer matrix, caused 50% inhibition of intrinsic transporter activity. However, this membrane perturbation had no significant effect on either the insulin dose-response curve (conducted at 37 degrees) or the time-course of the insulin stimulation of hexose transport (conducted at 32 degrees). These data are difficult to rationalize in terms of a model in which transport stimulation involves interaction of transporters and hormone-bound receptors that is limited by lateral diffusion of these proteins in the fluid lipid bilayer. Curve-fitting experimental insulin dose-response data for stimulation of 2-deoxy-D-glucose and D-glucose uptake provided an estimate of an insulin "association constant" for transport regulation that may be compared with recent insulin receptor binding data. Similar magnitude constants were obtained whether estimated directly from plots of transport velocity versus arithmetic hormone dose, or by extrapolation from linear segments of sigmoidal velocity versus log dose plots, or from inverse (Lineweaver-Burk-type) plots of the insulin dose-response data. Insulin apparently regulates transport by associating with a binding site, having an apparent dissociation constant which is determinable through kinetic measurements of hexose uptake (KDapp approx. 17-40 pM). This is in good agreement with the dissociation constant, KD, determined from Scatchard plots of recent binding data to adipocytes, for a class of receptors representing the "high affinity" binding sites for insulin. Insulin dose-response curve simulations also indicated that the stimulation process may be classified in pharmacologic terms as a typical graded biologic response and may involve insulin association with a site that regulates transport rates in a manner kinetically analogous to allosteric modulation of a V-series enzyme by a noncompetitive ligand. From the results we suggest that a relatively close association occurs between transport and receptor proteins in the membrane, where the relative activation of transport depends on the fractional occupancy of functional high affinity receptors by insulin, and the insulin stimulation of transport involves regions of the membrane that are not influenced significantly by

Adipose Tissue↗
PubMed1989

Co-administration of Ro 15-1788 prevents diazepam-induced retardation of recovery of function.

Following unilateral lesions of the anteromedial cortex, recovery from somatosensory asymmetry reliably occurs within about 10 days. Chronic exposure to diazepam significantly delays this recovery. In the present study, co-administration of Ro 15-1788, a benzodiazepine antagonist (i.e. it blocks the negative and positive allosteric modulation of GABA), prevented diazepam-induced retardation of recovery from somatosensory asymmetry. Nocturnal ambulatory (motor) activity was not different between rats receiving diazepam-alone and those receiving Ro 15-1788 in combination with diazepam. These data suggest that the benzodiazepine receptor is importantly involved in the detrimental effects of diazepam on recovery, and that non-specific behavior sedation plays little or no role.

Animals↗
PubMed1989

Modulation of glutamate receptors by phencyclidine and glycine in the rat cerebellum: cGMP increase in vivo.

In rats receiving N-methyl-D-aspartate (NMDA) intraventricularly or intracisternally the cerebellar cyclic guanosine monophosphate (cGMP) content increases in a dose-related manner. This response was used to study phencyclidine (PCP) and glycine interactions with the glutamate receptor subtype stimulated by NMDA. The increase of cGMP elicited by NMDA was inhibited by PCP and potentiated by glycine. Moreover, 2-amino-5-phosphonovalerate (APV) abolished the NMDA response. Since the increase in cerebellar cGMP induced by kainate, a synthetic agonist of another glutamate receptor subtype, was not modified by APV, the specificity of its action on NMDA response was confirmed. The increase of cerebellar cGMP content elicited by glycine was inhibited by PCP and APV but not by strychnine. Binding studies failed to demonstrate an apparent competitive interaction between PCP, glycine and NMDA. This suggests that the observed interaction is not of the isosteric type. The present results provide evidence that glycine, in vivo, acting at strychnine-insensitive recognition sites modulates allosterically in a positive manner the function of NMDA-sensitive glutamate receptors.

Amino Acids↗
PubMed1993

Electrophysiological characterization of excitatory amino acid responses in rat lateral parabrachial neurons in vitro.

The pontine parabrachial nucleus (PBN) is a major recipient of a diverse array of autonomic-related information from the caudal brainstem. Recent data indicate the presence of glutamate-like immunoreactivity within this nucleus. The effect of specific excitatory amino acid (EAA) receptor agonists and antagonists were studied in the lateral PBN (LPBN) by the use of whole-cell patch recordings in an in vitro brainstem slice preparation. Under current and voltage clamp conditions, independent bath applications of N-methyl-D-aspartate (NMDA; 10 microM), quisqualic acid (QUIS; 10 microM) and kainic acid (kainate; 10 microM) evoked membrane depolarization and an inward current in 28 of 31 LPBN neurons. In voltage clamp mode, the NMDA current (INMDA) was undetectable at potentials negative to -70 mV and a small inward current was observed at more depolarized potentials. However, in the absence of external Mg2+, the voltage dependence of INMDA was similar to that observed for QUIS and kainate. The allosteric modulation of the NMDA receptor by the strychnine-insensitive glycine binding site was examined by the application of the amino acid D-serine (0.5 mM). A marked and sustained potentiation of the steady-state INMDA (-60 mV holding potential) was observed. The selective NMDA-antagonist DL-2-amino-5-phosphonovaleric acid (APV; 10 microM) completely and reversibly blocked the NMDA-induced current, that was maximized in the absence of external Mg2+. Furthermore, this dose of APV was found to reversibly reduce the firing frequency of spontaneously active LPBN neurons.(ABSTRACT TRUNCATED AT 250 WORDS)

2-Amino-5-phosphonovalerate↗
PubMed1995

Pregnenolone sulfate potentiation of NMDA-mediated increases in intracellular calcium in cultured chick cortical neurons.

Pregnenolone sulfate (PS) has been reported to selectively augment glutamate-induced depolarizations mediated by the NMDA subtype of the glutamate receptor. The present study examines the ability of this neuroactive steroid to potentiate NMDA-mediated increases in intracellular calcium in cultured chick cortical neurons using the fluorescent dye Fura2. PS, in the absence of NMDA and glycine, significantly elevated intracellular calcium at 250 and 500 microM. This increase in free calcium was significantly attenuated at 250 microM PS by the prior addition of 50 microM CNQX, 10 microM dizocilpine or 1 microM nimodipine. NMDA and glycine, when added to the cells in saturating concentrations of 500 and 50 microM, respectively, consistently increased intracellular free calcium over baseline levels. In the presence of NMDA and glycine, both 50 and 100 microM PS produced a further significant rise in intracellular free calcium. The prior addition of CNQX, dizocilpine or both compounds together significantly inhibited this elevation in free calcium. The application of the endogenous polyamine spermine (250 microM) significantly potentiated the response of chick cortical neuronal cells to NMDA and glycine. PS, in the presence of NMDA, glycine and spermine, produced a further increase in intracellular free calcium at concentrations of 50 and 100 microM. The prior application of CNQX, dizocilpine or both compounds together significantly attenuated this rise in free calcium. These data confirm that PS is a positive allosteric modulator of the NMDA receptor and provide evidence that this neurosteroid does not interact with the polyamine modulatory site.

6-Cyano-7-nitroquinoxaline-2,3-dione↗
PubMed1995

Cardiovascular neurons in cat caudal ventrolateral medulla: location and characterization of GABAergic input.

The purposes of the present study were to: (1) characterize the GABAergic input to vasodepressor neurons in the caudal ventrolateral medulla of the cat, and (2) define more precisely the anatomical localization of these neurons in this species. This was done by microinjecting GABA receptor antagonists and agonists, and a negative allosteric modulator of the GABA receptor, namely, ethyl-beta-carboline-3-carboxylate, into the caudal ventrolateral medulla of alpha-chloralose-anesthetized animals while monitoring arterial blood pressure and heart rate. Localization studies where performed relating injection sites in the caudal ventrolateral medulla where cardiovascular responses were elicited, to neurons exhibiting immunoreactivity to tyrosine hydroxylase (TH) and phenethyl-N-methyl-transferase (PNMT). Microinjection of 1 and 10 ng of bicuculline into the caudal ventrolateral medulla produced decreases in mean blood pressure and heart rate of -34 +/- 6.4 and -49 +/- 9.2 mmHg, and -22 +/- 4.3 and -35 +/- 8.2 beats/min, respectively. Hypotension and bradycardia were also observed with picrotoxin microinjection (120 ng). Microinjection of muscimol (100-200 ng) and GABA (12 microgram) had no effect on mean blood pressure and heart rate. Microinjection of ethyl-beta-carboline-3-carboxylate also decreased mean blood pressure (-39 +/- 7.0 mmHg). The location of the micropipette tip after bicuculline microinjection in relation to TH and PNMT immunoreactive cells was as follows: (1) TH-immunoreactive cells of the A1 cell group were visible in the same relative location as the micropipette tip, and (2) no PNMT-positive cells were noted at the sites where bicuculline elicited hypotension. These results indicate that there is a tonic GABAergic input to neurons in the caudal ventrolateral medulla. The location of these neurons overlaps with the A1 cells.

Animals↗
PubMed1996

Enhancement of hippocampal acetylcholine release by the neurosteroid dehydroepiandrosterone sulfate: an in vivo microdialysis study.

The effect of dehydroepiandrosterone sulfate (DHEAS) administered i.p. on the release of acetylcholine (ACh) from the hippocampus of anesthetized rats was examined using in vivo microdialysis. DHEAS significantly increased ACh release above the pre-treatment levels for all doses tested. The administration of 100 mg/kg significantly enhanced ACh release greater than 4-fold when compared to the saline-treated group 80 min following drug administration. This study is the first to demonstrate that the neurosteroid DHEAS, a negative allosteric modulator of the GABAA receptor, can enhance the release of ACh from neurons in the hippocampus.

Acetylcholine↗
PubMed1990

Influence of nimodipine and diltiazem, alone and in combination, on phencyclidine-induced effects in rats: an EEG and behavioural study.

The influence of nimodipine and/or diltiazem on the EEG and behavioural effects induced by phencyclidine (PCP) was assessed in adult male Wistar rats. Nimodipine (2 and 10 mg/kg i.p.) and diltiazem (25-100 mg/kg i.p.) significantly potentiated both EEG (increase in background activity voltage, incidence of clustered slow waves) and behavioural (ataxia mean intensity) effects of PCP (5 mg/kg i.p.). A synergistic effect between low, ineffective doses of both nimodipine (0.5 mg/kg i.p.) and diltiazem (5 and 10 mg/kg i.p.) was also found. These data confirm the recent finding of a positive allosteric modulation existing between benzothiazepine (diltiazem) and dihydropyridine (nimodipine) binding sites. They also suggest that the modulation of calcium channels may play a pivotal role in the expression of PCP-induced effects.

Animals↗
PubMed1993

Intracellular protons control the affinity of skeletal muscle ATP-sensitive K+ channels for potassium-channel-openers.

Levcromakalim, a potential antihypertensive agent, is known to activate potassium channels dependent on intracellular ATP (K-ATP channels). In inside-out patches excised from frog skeletal muscle, levcromakalim or a related compound, SR 47063, caused a strong and persistent activation of K-ATP channels at a cytoplasmic pH of 7.1. However, at pH 6, these activators could no longer affect the K-ATP currents. Conversely, in the continuous presence of activator, lowering pH from 7.1 to 6 returned channel activity to its level in pH 6 alone. After wash-out of the activator, recovery from activation took minutes at pH 7.1 but only seconds at pH 6, thus ruling out an effect of protons on the activators in solution. These experiments suggest that K-channel-activators are unable to bind to their receptor when it is protonated, and more generally, they provide evidence at the microscopic level for proton-induced allosteric modulation of drug-receptor interaction.

Adenosine Triphosphate↗
PubMed1996

Fructose 2,6-bisphosphate induces irreversible transitions in cell-free extracts of rat liver.

The effect of fructose 2,6-bisphosphate on the dynamics of the 6-phosphofructo-1-kinase/fructose-1,6-bisphosphatase cycle is investigated in a cell-free extract of rat liver under steady-state conditions. Bistability emerges on the basis of the reciprocal allosteric modulation of 6-phosphofructo-1-kinase and fructose-1,6-bisphosphatase. Under conditions of bistability fructose 2,6-bisphosphate may cause transitions between alternative steady states. However, in contrast to what is frequently observed in bistable systems, within a broad range of experimental conditions these transitions proceed irreversibly from states with high ATP to states characterized by low ATP.

Adenosine Triphosphate↗
PubMed1992

Two tRNA-binding sites in addition to A and P sites on eukaryotic ribosomes.

The interaction of tRNA with 80 S ribosomes from rabbit liver was studied using biochemical as well as fluorescence techniques. Besides the canonical A and P sites, two additional sites were found which specifically bind deacylated tRNA. One of the sites is analogous to the E site of prokaryotic ribosomes, in that binding of tRNA is labile, does not depend on codon-anticodon interaction, does not protect the anticodon loop from solvent access, and requires the presence of the 3'-terminal adenosine of the tRNA. In contrast, the stability of the tRNA complex with the second site (S site) is high. tRNA binding to the S site is also codon-independent; nevertheless, the anticodon loop is shielded from solvent access. Removal of the 3'-terminal adenosine decreases the affinity of tRNA(Phe) for the S site approximately 50-fold. tRNA(Phe) is retained at the S site during translocation and through poly(Phe) synthesis. Thus, the S site does not seem to be an intermediate site for the tRNA during the elongation cycle. Rather, the tRNA bound to the S site may allosterically modulate the function of the ribosome.

Animals↗
PubMed1987

Effect of sodium ion on the affinity of naloxone for the kappa opioid receptor.

Several investigators have observed that sodium ion enhances the binding of naloxone to opioid receptors. This effect has generally been attributed to allosteric modulation of the state of the mu receptor. However, a recent claim has been made that the enhancement does not involve a change in the mu receptor, but instead occurs because naloxone becomes a more kappa-specific drug when sodium ion is present in high concentration. Since the claim was not based on experimental evidence from binding studies involving known high-affinity kappa ligands, we have investigated the competition of naloxone for the kappa site using [3H]U-69593 as the marker for receptor binding. Assays were carried out in the presence and absence of 100 mM NaCl. The results of the study indicate that sodium ion does not increase the affinity of naloxone or U-69593 for the kappa receptor.

Animals↗
PubMed1991

Diazepam binding inhibitor (DBI): a peptide with multiple biological actions.

Diazepam binding inhibitor (DBI) is a 9-kD polypeptide that was first isolated in 1983 from rat brain by monitoring its ability to displace diazepam from the benzodiazepine (BZD) recognition site located on the extracellular domain of the type A receptor for gamma-aminobutyric acid (GABAA receptor) and from the mitochondrial BZD receptor (MBR) located on the outer mitochondrial membrane. In brain, DBI and its two major processing products [DBI 33-50, or octadecaneuropeptide (ODN) and DBI 17-50, or triakontatetraneuropeptide (TTN)] are unevenly distributed in neurons, with the highest concentrations of DBI (10 to 50 microMs) being present in the hypothalamus, amygdala, cerebellum, and discrete areas of the thalamus, hippocampus, and cortex. DBI is also present in specialized glial cells (astroglia and Bergmann glia) and in peripheral tissues. In the periphery, the highest concentration of DBI occurs in cells of the zona glomerulosa and fasciculata of the adrenal cortex and in Leydig cells of the testis; interestingly, these are the same cell types in which MBRs are highly concentrated. Stimulation of MBRs by appropriate ligands (including DBI and TTN) facilitates cholesterol influx into mitochondria and the subsequent formation of pregnenolone, the parent molecule for endogenous steroid production; this facilitation occurs not only in peripheral steroidogenic tissues, but also in glial cells, the steroidogenic cells of the brain. Some of the steroids (pregnenolone sulfate, dehydroepiandrosterone sulfate, 3 alpha-hydroxy-5 alpha-pregnan-20-one, and 3 alpha, 21-dihydroxy-5 alpha-pregnan-20-one) produced in brain (neurosteroids) function as potent (with effects in the nanomolar concentration range) positive or negative allosteric modulators of GABAA receptor function. Thus, accumulating evidence suggests that the various neurobiological actions of DBI and its processing products may be attributable to the ability of these peptides either to bind to BZD recognition sites associated with GABAA receptors or to bind to glial cell MBRs and modulate the rate and quality of neurosteroidogenesis. The neurobiological effects of DBI and its processing products in physiological and pathological conditions (hepatic encephlopaty, depression, panic) concentrations may therefore be explained by interactions with different types of BZD recognition site. In addition, recent reports that DBI and some of its fragments inhibit (in nanomolar concentrations) glucose-induced insulin release from pancreatic islets and bind acyl-coenzyme A with high affinity support the hypothesis that DBI isa precursor of biologically active peptides with multiple actions in the brain and in peripheral tissues.

Amino Acid Sequence↗
PubMed1993

Is PP56 (D-myo-inositol-1,2,6-trisphosphate) an antagonist at neuropeptide Y receptors?

PP56 (D-myo-inositol-1,2,6,-trisphosphate) has been reported to specifically inhibit neuropeptide Y-mediated effects in vasculature, heart and brain; because of its reversible but non-competitive antagonism interaction with neuropeptide Y receptor signalling or allosteric modulation of neuropeptide Y binding have been postulated. These possibilities were tested in the present study. PP56 did not affect [125I]neuropeptide Y binding to HEL- or SK-N-MC-cells or to porcine splenic membranes. PP56 did not inhibit neuropeptide Y-stimulated Ca2+ increases in HEL- or SK-N-MC-cells or in cultured porcine aortic vascular smooth muscle cells but if anything slightly enhanced it. PP56 did not antagonize the neuropeptide Y-mediated inhibition of forskolin-stimulated cAMP accumulation in HEL-cells. We conclude that previously reported antagonistic effects of PP56 occur distal to the neuropeptide Y receptor or its second messenger systems Ca2+ and cAMP or may be restricted to neuropeptide Y receptors in certain model systems.

Animals↗
PubMed1995

ATP enhances catecholamine uptake into PC12 cells.

Catecholamine uptake into PC12 cells, in the presence and absence of ATP, was measured in a bicarbonate-buffered Krebs Ringer. ATP enhanced significantly the uptake in a dose-dependent manner with maximal uptake at 1-3 mM. ATP increased the Vmax of uptake by 3-5 fold for both dopamine and norepinephrine, without a significant change in the Km. ATP-stimulated amine uptake was temperature- and Na(+)-dependent and robust in bicarbonate, but not in HEPES buffer. The ability to enhance uptake was not observed with metabolites of ATP. GTP and UTP were equally effective to ATP in enhancing CA uptake. This uptake was less sensitive to uptake inhibitors in bicarbonate buffered media than in phosphate-buffered media, and more so in the presence of ATP. It is suggested that ATP is an allosteric modulator of the transporter and that a stable ATP analog, with ATP-like enhancement of dopamine uptake, may be an effective cocaine antagonist.

Adenosine Triphosphate↗
PubMed1987

Isolation from rat brain tissue of an inhibiting activity for dihydropyridine binding sites and voltage-dependent CA2+ uptake.

Nitrendipine binding-inhibitory activity was extracted and partially purified from rat brain. This preparation also decreased veratridine-stimulated Ca2+ uptake in cultured cerebellar granule cells. It failed to inhibit 3H-nitrendipine binding by sequestering Ca2+ that is required for the high affinity binding of nitrendipine. An allosteric modulation of nitrendipine recognition sites by this preparation is suggested.

Animals↗
PubMed1987

gamma-Hydroxybutyric acid binding sites: evidence for coupling to a chloride anion channel.

The effect of eight anions, including chloride, on the binding of gamma-hydroxy[2,3-3H]butyric acid (GHB) to synaptosomal membranes of rat and human brain was ascertained, as was the effect of a number of other allosteric modulators of the GABA/benzodiazepine/picrotoxin complex. All ions which were active at the chloride ion channel, inhibited the binding of [3H]GHB in a dose-dependent manner, with maximum inhibition of binding being 60% of 300 mM concentration of anion. Inactive ions in this binding system included sulfate, acetate and fluoride, all impermeable to the chloride ion channel. The inhibition of binding was temperature-dependent, being abolished at 37 degrees C and was independent of the cation used. The binding of [3H]GHB was also enhanced by pentobarbital, picrotoxin and diazepam but unchanged in the presence of GABA, muscimol, bicuculline, baclofen or strychnine. These data raise the possibility that the epileptogenic effect of GHB may be modulated by an action on the chloride ion channel, that is tightly coupled to the GABA/benzodiazepine/picrotoxin and/or GHB receptor complex.

Adult↗